The optical inspection of external, exterior, or outer surfaces and/or structures of components such as semiconductor die or packaged semiconductor devices for defects can be performed by way of “five side inspection.” Five side inspection involves directing illumination toward five sides of a component, such as a component bottom surface and four component sidewalls, when the component is held (e.g., by a pick and place device) on a sixth side, which in accordance with this definition of sides would be the component's bottom. In association with five side optical inspection, illumination can be directed to the component's bottom surface to facilitate the capture of a bottom surface image; and illumination can be directed to the component's sidewalls to facilitate the capture of component sidewall images. Incident illumination that is reflected from the component's bottom surface and/or sidewalls can be redirected toward an optical assembly such as a lens assembly and an image capture device for image capture purposes.
FIG. 1A is a schematic illustration showing portions of a conventional five side inspection apparatus, in which a component 20 is held by a component holder 50 (e.g., a pick-and-place device) in a bottom surface inspection position such that the component vertically resides at a bottom surface inspection position, above as well as between a set of reflectors or prisms 130a-b. While FIG. 1A illustrates only two prisms 130a-b, a typical five side inspection system includes four prisms 130, i.e., a prism corresponding to each of four sidewalls of the component.
A brightfield illuminator 100 outputs brightfield illumination in an upward direction, which passes through a beam splitter 110 as the brightfield illumination travels toward the component 20. Some of the brightfield illumination reaches and is reflected by a component bottom surface and/or surface features corresponding thereto, such as solder balls, and is directly reflected thereby in a downward direction toward the beam splitter 110. Upon reaching a reflecting surface 112 of the beam splitter, this downwardly traveling brightfield illumination is redirected toward an image capture device (not shown) such that an image corresponding to the component bottom surface can be captured.
Some of the brightfield illumination output by the brightfield illuminator 100 additionally reaches each prism 130a-b. Lateral optical paths between the prisms 130a-b are not blocked or obstructed by the component 20 because the component is disposed above the prisms 130a-b. Thus, upon reaching any given prism 130a-b, the brightfield illumination is redirected in a lateral direction toward an opposing prism 130b-a, after which the brightfield illumination is again redirected in a downward direction toward the beam splitter 110. Upon reaching the beam splitter's reflecting surface 112, this illumination which had travelled along an optical path through the prism 130a-b is further redirected toward an image capture device, and forms outer portions of the image captured thereby.
FIG. 1B is a representative inspection image corresponding to a component bottom surface captured while the component is held in a bottom surface inspection position corresponding to the inspection configuration shown in FIG. 1A. As indicated in FIG. 1B, brightfield illumination that had passed through the prisms 130a-b appears as bright or very bright peripheral portions of the captured image, and the component's bottom surface and structures corresponding thereto appear within an in-focus central region of the captured image.
After image capture is has occurred when the component is held at the bottom surface inspection position, the component holder 50 vertically lowers or plunges the component 20 to a sidewall inspection position, such that the component 20 resides between the prisms 130a-b and the component's sidewalls fall within the lateral optical paths between the prisms 130a-b. Thus, when the component is disposed at the sidewall inspection position, the component 20 acts as an obstruction relative to some illumination traveling from one prism 130a-b toward the other prism 130b-a. 
More particularly, FIG. 1C is a schematic illustration showing portions of the conventional five side inspection apparatus, in which the component 20 is held by the component holder 50 at a sidewall inspection position, such that the component's vertical extent or height/thickness falls within the bounds of the vertical extent or height of the prisms 130a.b. As before, when the brightfield illuminator 100 outputs brightfield illumination, the brightfield illumination passes through a beam splitter 110 as the brightfield illumination travels in an upward direction toward the component 20. Some of the brightfield illumination reaches and is reflected by the component's bottom surface and/or surface features corresponding thereto, such as solder balls, and is directly reflected thereby in a downward direction toward the beam splitter 110. Upon reaching a reflecting surface 112 of the beam splitter 110, this downwardly traveling illumination corresponding to the component bottom surface is redirected toward an image capture device.
Some of the upwardly traveling brightfield illumination additionally reaches the set of prisms 130a-b. The prisms 130a-b reflect and redirect this brightfield illumination such that is travels laterally toward the component sidewalls. A portion of this laterally traveling illumination is reflected by the component sidewalls back toward the prisms 130a-b, which then reflect and redirect this illumination in a downward direction to the beam splitter 110, whereupon the beam splitter's reflecting surface 112 redirects this illumination that has been reflected by the component sidewalls toward the image capture device, such that images corresponding to each of the component's sidewalls can be captured, simultaneous with the capture of illumination corresponding to the component bottom surface/bottom surface structures while the component is positioned at the sidewall inspection position.
FIG. 1D is a representative inspection image captured while a component 20 is held at a sidewall inspection position, in which a central image region corresponds to brightfield illumination reflected by the component's bottom surface and/or structures carried thereby, and individual image regions at the left, right, bottom, and bottom of the image correspond to the component's sidewalls.
The image that is captured while the component 20 is held at the bottom surface inspection position provides a central in-focus image region corresponding to the component's bottom surface, and provides bright peripheral regions that contain or convey essentially no useful information about the component's sidewalls. The image that is captured while the component 20 is held at the sidewall inspection position provides in-focus peripheral image regions corresponding to the component sidewalls, and an at least slightly defocused central image region corresponding to the component bottom surface. This defocusing of the central image region within the image captured while the component 20 is held at the sidewall inspection position occurs as a result of the vertical offset between the bottom surface inspection position and the sidewall inspection position.
In particular, the vertical offset between the bottom surface inspection position and the sidewall inspection position is selected such that optical path lengths between the component's front surface and/or structures carried thereby (e.g., solder balls) and the image capture device's imaging plane are equal or approximately equal to optical path lengths between the component's sidewalls and the image capture device's imaging plane. As a result, no (re)focusing operation needs to occur between the capture of an image when the component 20 is plunged from the bottom surface inspection position to the sidewall inspection position, which aids inspection throughput.
For inspection purposes, a single composite image is typically created from the image captured while the component 20 was held at the bottom surface inspection position and the image captured while the component 20 was held at the sidewall inspection position. This composite image is generated by way of combining or digitally “stitching” together (a) the in-focus central region of the image captured while the component 20 was held at the bottom surface inspection position, corresponding to the component bottom surface, with (b) the in-focus peripheral or outer regions of the image captured while the component 20 was held at the sidewall inspection position, corresponding to the component sidewalls. FIG. 1E provides a representative composite image generated by way of combining or digitally stitching together central and peripheral portions of the bottom surface inspection image and the sidewall inspection image, respectively. FIG. 1F illustrates a portion of the composite image corresponding to a component sidewall.
In a conventional five side inspection apparatus, the vertical extent of the prisms 130 significantly exceeds the vertical extent of the component's sidewalls. Consequently, when a component 20 is positioned at the sidewall inspection position, upwardly traveling brightfield illumination output by the brightfield illuminator 100 which is incident upon the prisms 130 and which is directed or reflected by the prisms 130 toward the component sidewalls is vertically distributed across a spatial extent or area greater or significantly greater than the vertical extent of the component's sidewalls. Thus, a significant amount of brightfield illumination output by the brightfield illuminator 100 which has been redirected along a lateral path by a given prism 130 does not fall upon a component sidewall, and thus misses or bypasses the component entirely. Such brightfield illumination simply travels unobstructed to an opposite prism 130, and is reflected along a downward path to the beam splitter 110 whereupon it forms a portion of a captured image in which this brightfield illumination that had followed a direct prism-to-prism optical path appears as a brightly lit white background against the captured image of the component sidewalls, as indicated in FIG. 1D.
Such brightfield illumination that was directed along a lateral optical path perpendicular to a component sidewall, but was never incident upon component sidewalls and which instead simply experienced multiple prism reflections along optical paths that did not involve reflection from the component itself or structures associated therewith carries no optical information regarding component defects. Such illumination can therefore be referred to as extraneous brightfield illumination. This extraneous brightfield illumination is sufficiently intense or bright that its presence in a captured sidewall image can give rise to “optical crosstalk” that can visually “wash out” the appearance of shadows or very small defects (e.g., micro-defects such a hairline cracks or fractures) in sidewall images, thereby interfering with or limiting the extent to which image processing algorithms can detect micro-defects on component sidewalls. In other words, this extraneous brightfield illumination can decrease the contrast and sharpness of captured sidewall images. This is extremely significant since integrated circuits are increasingly getting smaller, and associated defects are also smaller, thereby increasing the need for improved image contrast and sharpness. Optical crosstalk tends to reduce the visibility and optical resolution or clarity of very small cracks (e.g., especially cracks having a size or dimension of less than or equal to approximately 10 μm).
A need exists for improving the manner in which component sidewalls are illuminated and component sidewall images are captured in five side inspection apparatuses.